In recent years, zoom lenses have come into common use in photographic optical systems for use in still cameras, video cameras, and the like; in particular, cameras employing so-called high-zoom lenses wherein zooming ratios are in excess of three are rapidly becoming standard equipment.
Particularly with integral-lens-type cameras, wherein the photographic optical system is integral with the camera main body, importance is placed on portability, and there have accordingly been a variety of proposals pertaining to zoom lenses suitable for applications permitting reduction in size and weight.
Specifically, positive-positive-negative three-group-type lenses (consisting of, in order from the object side, a positive lens group, a positive lens group, and a negative lens group) and positive-negative-positive-negative four-group-type lenses (consisting of, in order from the object side, a positive lens group, a negative lens group, a positive lens group, and a negative lens group) are known as variable-magnification optical systems that are small in size and that are suitable for high zooming ratio.
For example, Japanese Laid-Open Patent Application (Kokai) No. H2 [1990]-73211 and the like are known as examples of positive-positive-negative three-group-type lenses, while Japanese Laid-Open Patent Application (Kokai) No. H2[1990]-207210, Japanese Laid-Open Patent Application (Kokai) No. H6[1994]-265788, and the like are known as examples of positive-negative-positive-negative four-group-type lenses.
Furthermore, the positive-negative-positive-positive-negative five-group-type lens disclosed in Japanese Laid-Open Patent Application (Kokai) No. H7[1995]-27979 is known.
However, there has been the problem that an increase in zooming ratio is accompanied by an increase in focal length, causing the length of the overall lens to become large and adversely affecting portability.
Furthermore, with the positive-positive-negative three-group-type lens, due to the fact that above a zooming ratio of three the lateral magnification of the negative lens group becomes large when in the extreme telephoto state, it is necessary that the positional accuracy of the several lens groups be made extremely precise, with the result that lens performance deteriorates markedly because of the influence of stopping precision. In particular, because of the need to increase the lateral magnification of the negative lens group in order to achieve small size, it has been difficult to simultaneously achieve both small size and high performance.
With the positive-negative-positive-negative four-group-type lens, because of the increased number of movable lens groups the lateral magnification of the negative lens group arranged nearest to the image plane is relaxed i.e., is lessened when in the extreme telephoto state, and, while the zooming ratio might be high and it may be possible to achieve small size and high performance, it has not been possible to achieve adequate wide-angle performance.
While the positive-negative-positive-positive-negative five-group-type lens better permits attainment of high zooming ratio and small size while maintaining high performance as compared with the aforementioned four-group-type lens, because of the large widths of the several lens groups in the direction of the optical axis it has been difficult to achieve improved camera portability.
The object of the present invention is to solve the aforementioned problems and to provide a variable-focal-length lens system that is small in size and that is suitable for applications having a high zooming ratio while maintaining high performance.